11. Transport of oxygen and carbon dioxide in the blood

Question 1

Structure of Hb

Answer 1

4 polypeptide chains
2 x α and 2 x β chains
Each chain assoc with a haem group
(contains a ferrous ion; Fe2+)

Question 2

Function: oxygen ‘carrier’

Answer 2

Each haem can bind 1 O2 molecule

Each Hb molecule therefore carries 4 O2 molecules

Question 3

INCREASED affinity for O2:

change in Oxygen dissociation curve

Answer 3

Left shift

Question 4

DECREASED affinity for O2:

change in Oxygen dissociation curve

Answer 4

Right shift

Question 5

Special adaptations of Fetal Haemoglobin (HbF)

Answer 5

Different polypeptide chains in the global:
α2γ2 (causes a left shift)

O2 affinity higher with HbF

HbF will pick up O2 from maternal HbA at a given PO2

Question 6

Gradual replacement of HbF with HbA after birth (months)

Advantage:

Answer 6

easier release of O2 to tissues

Less tissue hypoxia

Question 7

Persistence of HbF

Answer 7

Thalassaemia

Tx: blood transfusions

Question 8

Physiological changes that cause a Rightward shift (reduced affinity)

Answer 8

Increased temperature
Decreased pH (protonation; Bohr effect)
Increased CO2 levels (direct and via H+)
Increased 2,3-diphosphoglycerate (2,3-DPG)

Question 9

CO2 Modes of transport

Answer 9

Solution in water = 10%
Carbamino compounds = 30%
Bicarbonate (HCO3-) = 60%

Question 10

From CO2 to HCO3-

Answer 10

CO2 enters the RBC by diffusion down a partial pressure gradient

Carbonic anhydrase (CA) converts CO2 to carbonic acid

H2CO3 rapidly dissociates to hydrogen ions and bicarbonate ions

Bicarbonate is transported out of the RBC

Chloride shift

H+ binds to oxyHb and lowers its affinity for O2… O2 is delivered to the tissues (Bohr effect)

Increased ability of deoxygenated blood to carry CO2 (Haldane Effect)